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Polyhydroxyalkanoates (PHAs) are sustainable, versatile, biocompatible, and bioresorbable polymers that are suitable for biomedical applications. Produced via bacterial fermentation under nutrient-limiting conditions, they are uncovering a new horizon for devices in biomedical applications. A wide range of cell types including bone, cartilage, nerve, cardiac, and pancreatic cells, readily attach grow and are functional on PHAs. The tuneable physical properties and resorption rates of PHAs provide a toolbox for biomedical engineers in developing devices for hard and soft tissue engineering applications and drug delivery. The versatility of PHAs and the vast range of different PHA-based prototypes are discussed. Current in vitro , ex vivo , and in vivo development work are described and their regulatory approvals are reviewed. Polyhydroxyalkanoates (PHAs) are polymers produced sustainably via bacterial fermentation under nutrient-limiting conditions. Both the degradation profile and the mechanical properties of PHAs can be tuned. PHA-based scaffolds have demonstrated excellent biocompatibility with a wide range of cell types including but not limited to bone, cartilage, nerve, cardiac, and pancreas, and have exhibited no notable cytotoxicity or inflammatory and immune responses in vivo. The FDA has approved poly(4-hydroxybutyrate) for use in biomedical applications, and this is already widely used in sutures and hernia meshes in the clinic. Recent advances in processing have shown that PHAs have high potential for use as the base material in a large variety of biomedical prototypes including wound-healing patches, cardiac patches, heart valves, bone scaffolds, cartilage scaffolds, and nerve guidance conduits. [ABSTRACT FROM AUTHOR]

Natural biomaterials have benefited the human civilisation for millennia. However, in recent years, designing of natural materials for a wide range of applications have become a focus of attention, spearheaded by sustainability. With advances in materials science, new ways of manufacturing, processing, and functionalising biomaterials for structural specificity has become feasible. Our review is focused on bacterial cellulose (BC), an exceptionally versatile natural biomaterial. BC is a unique nanofibrillar biomaterial extruded by microscopic single- cell bacterial factories utilising the chemical energy harvested from renewable substrates. BC is extracellular and is intrinsically pure, unlike other biopolymers that require extraction and purification. BC fibres are 100 times thinner than plant-derived cellulose and exist in a highly porous three-dimensional network that is highly biocompatible. Macro fibres fabricated from BC nanofibrils are stronger and stiffer, have high tensile strength values and can be used as substitutes for fossil fuel-derived synthetic fibres. The increased surface area to volume ratio allows stronger interactions with the components of composites that are derived from BC. The reactive hydroxyl groups on BC allows various chemical modifications for the development of functionalised BC with a plethora of 'smart' applications. In this review we consolidate the current knowledge on the production and properties of BC and BC composites, and highlight the very recent advancements in bulk applications, including food, paper, packaging, superabsorbent polymers and the bio-concrete industries. The process simplicity of BC production has the potential for large scale low-cost applications in bioremediation. Furthermore, the emerging high value applications of BC will be in electrochemical energy storage devices as a battery separator, and in transparent display technologies will be explored. Finally, the extensive biomedical applications of BC are discussed including, wound healing, controlled drug delivery, cancer treatment, cell culture and artificial blood vessels. In a further development on this, additive manufacturing considers enhancing the capabilities for manufacturing complex scaffolds for biomedical applications. An outlook on the future directions of BC in these and other innovative areas is presented. [ABSTRACT FROM AUTHOR]